Billets emerging from a steel mill typically have a surface layer of imperfections or scale, as well as a number of spaced-apart, fairly deep cracks. If the billets are sent directly to a rolling mill, the defects are reproduced in the finished product. Consequently, the surface layer or scale is removed from the billets in a "skinning" procedure in which the billet reciprocates beneath a grinding wheel which removes a thin layer from the surface of the billet. Modern skinning machines operate automatically, with the grinding wheel automatically reciprocating between the ends of the billet and the grinding wheel pressure being automatically adjusted.
After the automatic skinning procedure has been completed, the cracks and deep imperfections remain. These defects are normally manually removed with a grinding wheel in a procedure known as "spotting."
Attempts have been made to automate the spotting procedure in the same manner as the skinning procedure. However, skinning of the billet is uniform about the entire surface of the billet. The skinning procedure thus lends itself to automation. Unlike the skinning procedure, the spotting procedure introduces a number of random variables, such as the location, size, shape and depth of the defects. These random variables have heretofore prevented the automatic spotting of billets and the like.
Prior attempts to design automatic spotting machines have generally used magnetic or optical flaw detectors having a known position in relation to the billet to generate a record of the location of all defects on the billet. The record may then be used by an automatic grinding machine to grind each of the defects. Alternatively, the position of the defects may be entered by manual means in order to control the operation of a grinder such as disclosed in U.S. Pat. No. 3,822,632.
These previous attempts to determine the locations of defects have generally not been successful because it is difficult for the sensors to accurately determine the depth of the defect as well as its size and shape, particularly when the shape of the defect is geometrically complex. As a result, information concerning the defect must be entered manually; but no system has been devised for allowing such information to be easily and quickly entered by manual means. Furthermore, other manual defect entry devices allow only the location of the defect to be entered, but not their size, shape and depth.